Metered dose dispensers, in particular pressurized metered dose dispensers, have had a major role in for example the treatment of asthma and other conditions since they were introduced nearly half a century ago. Moreover, the use of metered dose medicinal dispensers is becoming an increasingly important method of administering medicaments to a patient e.g. to the lung, nasal and/or buccal cavities or sublingually.
The medicament is generally formulated with suitable propellant and if appropriate other components and charged into a container, e.g. an aerosol vial. The container is typically fitted by means of a ferrule with a dispensing means, such a valve, in particular a metered dose valve, comprising an elongate outlet member (e.g. a valve stem) movable between closed and discharged positions, to provide a dispensing canister. The dispensing canister is typically used in conjunction with an actuator, typically having a patient port, for example a mouthpiece or a port adapted for nasal use. The actuator typically comprises a support block having a socket adapted to receive the outlet member of the dispensing means and an orifice having open communication with the socket and the patient port. The container and the support block are reciprocally movable relative to each other to allow the outlet member to move to its discharge position during the operation or firing of the device, thereby dispensing a dose. The adaptor also typically includes an elongate or generally cylindrical portion extending opposite the support block and providing a chamber to house at least a portion of the container. To facilitate locating and supporting the proper alignment of the container within the chamber, typically the chamber is provided with one or more ribs. There are many critical design features of the actuator and the dispensing canister, in particular in relation to one another, in order to achieve the necessary and/or desirable medicinal dispensing performance. For example, for metered dose inhalers, the design of the airflow passage through the actuator entraining the spray is taken into account to facilitate the provision of the required and/or desired and/or consistent in vitro dose delivery and respirable fraction.
A difficulty arising from use of metered dose medicinal devices is that the patient often cannot precisely determine the amount of medicament in the container at any given time. In extreme cases, a patient, possibly in an emergency situation and requiring an immediate dose of medicament, may find that the container will not dispense a dose because its contents have already been exhausted.
A number of dose counters, as an add-on component for metered dose medicinal products to be mounted onto the closed end of the container of the dispensing canister, have been proposed, e.g. in WO 95/26769, WO 95/08484, WO 96/03172, WO 96/39337, WO 99/57019, U.S. Pat. No. 5,622,163 and U.S. Pat. No. 5,871,007.